This wood movement calculator estimates how much a board will expand and contract across its width as humidity changes through the year. Wood is hygroscopic — it gains and loses moisture with the seasons — and ignoring that movement is the fastest way to crack a panel or seize a drawer.
How wood moves
Wood barely changes in length but moves significantly across the grain. The amount depends on the species (each has a tangential and radial movement coefficient), the change in moisture content between seasons, the board's width, and how it was sawn — flatsawn boards move more across their width than quartersawn ones. The calculator multiplies the board width by the species coefficient and the expected moisture-content swing to estimate the seasonal change.
Moisture content tracks the relative humidity of the surrounding air. A board might sit near 7–8% in a heated home in winter and rise to 11–12% in a humid summer, and that few-percent swing is enough to move a wide panel by a noticeable fraction of an inch.
Designing for movement
Good construction lets wood move rather than fighting it: floating panels in frame-and-panel doors, breadboard ends fixed at one point only, slotted screw holes for tabletops, and finishes applied to all faces to slow moisture exchange. Estimating the likely movement up front tells you how much clearance and how many slots you need to build in.
A 12-inch-wide flatsawn oak panel will see its moisture content swing about 4% between winter and summer (oak tangential movement ≈ 0.0037 per 1% MC).
- Movement per inch of width per 1% MC change ≈ 0.0037 in (flatsawn oak).
- Total = 0.0037 × 12 in width × 4% MC change ≈ 0.18 in.
Expect roughly 3/16 inch of seasonal movement across the panel — build in clearance to suit.
